Laminated denture



LA MAR wHARms LLOYD w. coLToN ma (LWL LA MAR W. HARRIS ET AL l LAMINATED DENTURE Filed Oct. 23, 1945 Apf 15, 1947.

Patented Apr. 15, 1947 LAMINATED DENTURE La Mar w. Hari-is and Lloyd w. Colton,

United States Navy Application October 23, 1945, Serial No. 624,006

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) Claims.

This invention relates to artificial dentures and particularly to laminated dentures prepared in part from acrylic resins.

The shortcomings of acrylic resins such as polymerized methyl methacrylate as. denture bases have been recognized for some time by the dental profession. The primary shortcoming is the lack of dimensional stability; that is, there is a pronounced tendency to warp and change shape. In the molding process, it has been found impossible to mold methacrylate resins to flt a metal base, the molded plastic always warping to some extent and leaving the mold. Also, there may be fur.- ther changes that occur in the mouth in a few weeks time, due in part to the absorption of water. Acrylic resins possess a relatively low teisile strength, and for this reason fractures are common in partial dentures made of this resin, and full dentures are often broken when subjected to stress. However, other lproperties of acrylic resins make it desirable above all other known denture bases at the present time.

In general, the object of this invention is to take advantage of the desirable properties of acrylic resins while overcoming the disadvantages of such resins so as to provide strong, dimensionally stable dentures which do not warp and leave the mold and which will retain the same t after months of wear in the mouth.

In accordance with this invention, the water absorption of an acrylic resin, such as polymerized methyl methacrylate,l is reduced by admixing with another resin having a low water absorption coeicient, and the strength and dimensional stability are increased by reinforcement and lamination. To reduce water absorption, polystyrene is preferred. Methyl methacrylate has a water absorption coefficient of over 0.5%, while the water absorption of polystyrene is so low as to be practically immeasurabie with standard test equipment. Mixtures of methyl methacrylate and polystyrene have much lower water absorption coefficients than methyl methacrylate alone. However, the color instability of polystyrene makes it advisable to use'this plastic only on the tissue side of'the denture, and it is preferred to use methyl methacrylate on all exposed surfaces.

In preparing polymeric mixtures of the type herein contemplated, it is preferred to mix monomeric styrene with monomeric methyl methacrylate and then add polymeric methyl methacrylate in powdered form in such proportions as to yield a doughy mass upon standing. The doughy mass is readily packed into the denture mold to form the tissue side of the denture, and is cured in conjunction with other plastics and reinforcing materials as described below.v

While various reinforcing materials may be fused, it has been found that fibrous materials offer many advantages, and, in particular, a woven fabric of ber glass imparts great strength, rigidity, and permanence to the nal article. Fiber glass cloth impregnated with a modified vinyl butyral, preferably in the proportions' of about 25% t0. about 35% by volume of the cloth, has been found to be most suitable. The presence of free hydroxyl groups in a partial vinyl butyral resin improves its adhesion to the glass fibers and to outer laminations. Such partial vinyl butyral resins may suitably be modified to a'curingor thermosetting form by adding from about 17% to about preferably 25%, of a phenol-formaldehyde resin. For impregnation, the modified vinyl butyral is dissolved in an organicsolvent, such as a mixture of ethyl acetate and ethyl alcohol. Other reinforcing materials such as duck fabric may be used, but glass fabric is much to be preferred because of its low water absorption. Certain ofthe light weight, stainless alloy metals may be used as reinforcing materials,

either in cast sheet form or in the form of a` woven metal4 gauze or fabric. For example, an alloy comprising cobalt, chromium and nickel in various proportions, may be used to advantage.

For a more complete understanding of the invention, reference is made to the drawing, illustrating one embodiment ofI the invention, in

. which:

Figure 1 is a top plan view of a denture, and Fig. 2 is a vertical sectional view taken on the line 2 2 of Figure 1.

prising a mixture oi acrylic resin and polystyrene,

which layer is bonded tothe upper surface of the reinforcing material I0. On the exposed side of the denture, is an acrylic layer I2 which is bonded to the lower surface of the reinforcing material i0. The mixed plastic layer Il merges with plastic layer i2 at the edge i3 of the denture, thus sealing the reinforcing layer I0 within .the body of the denture.

A lamination in commotion with In preparing dentures of the type illustrated in the drawing, utilizing ber glass or other fabric as the reinforcing material, the fabric is first impregnated by immersion in a solution of modi- -fied polyvinyl butyral resin, preferably comprising '15% polyvinyl butyrai and 25% phenol formaldehyde resin, then running the fabric through rolls to express the excess of resin until the fabric contains from 25% to 35% by volume of the resin, and then drying at about 165 F. until there are no signs of tackiness. The impregnated fabric is then cut into blanks of the approximate size to flt denture bases. To Vprepare the blank for plastic materials, it is immersed in boiling water until softened sufficiently to allow its adaptation to the cast side of a denture flask before any packing is done. It is then removed and carefully trimmed to two or three millimeters short of the periphery, re-adapted, chilled, and set aside until needed.

Fiber glass identified in the trade as E. C. C. 164

is one example of a suitable glass fabric, but the size of the mesh can be varied from a very line mesh to an even coarser mesh. The termv E. C. C." means electrical continuous clot and the number following the term indicates the warp. Particularly good results are obtained by impregnating two separate layers of E. C. C. 116 liber glass and inserting them into the denture at cross warp, in direct contact with each other.

In molding the laminated denture of this invention, the case is first invested, either for compression or injection molding, in the manner well known in the art. The -wax is boiled out and the investment is thoroughly ing water. If the separating medium is pure tinfoil, the wax set-up will have been tinfoiled before the investment was placed in the upper half of the flask. After separating and cleaning, the cast side is carefully foiled and the case is ready for packing. If, however, one of the alginate preparations is used as the separating medium, it is applied to both halves of the ilask after the case is cleaned and has stopped steaming. vWhen dry the case is ready to be packed.

Before starting the actual packing, it is necessary to place over the cast side a spacing material which will determine and control the desired thickness of the mixed plastic layer Il of the denture. proximately one half the thickness of the palatal area and may be: (l) Ashs tray metal No. 7, burnished to the cast to the exact peripheral line;A (2) a sheet of base plate wax adapted and trimmed to the exact peripheral line; or (3) a piece of damp blotting paper adapted and trimmed in the same manner. When this is securely in place, the previously prepared liber glass blank should be tted to the cast and then removed.

The first resin to be packed is the acrylic resin. Suitable resins of this type are commercially available, tinted and otherwise prepared for ready use. For example, powdered polymerized methyl methacrylate is mixed in suitable proportions with monomeric methyl methacrylate and allowed to stand until the mixture is putty-like. The usual proportions are one part of monomer to about three or four parts of polymer. The putty-like mixture is packed, in excess, in the tooth side of the flask. Two sheets of dampened Cellophane are placed over the resin, a trial closure is made, and the flask is then opened to remove the excess resin and ilash.

At this stage, the spacing material is removed flushed with clean boil- This spacing material should be apand discarded. About the same amount of the mixed plastic, comprising polystyrene and methyl methacrylate, as the bulk of the spacing material is adapted to the cast side of the flask. This mixed plastic may be prepared by mixing about of monomeric styrene and about 20% of monomeric methyl methacrylate, and then mixing the liquid thus formed with powdered polymeric methyl methacrylate, in the proportions of about one part of liquid to about four parts of powdered polymer. .After thorough mixing, the mixture is allowed to stand until-'it is doughy or putty-like. After packing this .mixture in the cast side of the flask, two sheets of dampened Cellophane are placed over it, and a trial closure is made, followed by removal of excess and ods are: (l) `Place the flask in water at room temperature, raise the temperature at the rate of two degrees per minute, and then boil for at least 45 minutes, or (2) place the flask in water at F. for three hours and then boil for at least 45 minutes.

The finished denture is a stable product, which does not leave the mold and which will fit a metal die. There is no distortion of the denture base, as was usually the case with acrylic resins alone, said distortion of acrylic resins being probably caused by the release of internal strains. By laminating and processing four different resins at the same time, according to the process of this invention, it appears that four distinctly different strain patterns may be formed which counteract each" other and give stability to the finished product. Some of the important differences in physical properties'of the laminated product of this invention, utilizing fiber glass E. C. C. 164 as the reinforcing material, are listed in the following table.

When other fibrous materials are' used instead of fiber glass, the laminated product shows great improvements over the unlaminated products of the prior art, although th'e improvements are not as great as in the case of the ilber glass laminates.

Obviously, many modifications and variations of the invention, as hereinbefore disclosed, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

Th'e invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

We claim:

1. A laminated denture comprising a portion of glass fabric, impregnated with a modified vinyl butyral, a portion of acrylic resin bonded to said fabric on the exposed side of the denture, and a portion comprising a mixture of acrylic resin and polystyrene, bonded to said fabric on the tissue side of the denture.

2. The laminated denture of claim 1 wherein said acrylic resin is vpolymerized methyl methacrylate.

3. The laminated denture of claim 1 wherein said modied vinyl butyral comprises vinyl butyral and from about 17% to about 70% of phenol formaldehyde.

4. A laminated denture comprising a reinforcing layer of glass fabric, impregnated with' a vinyl butyral resin modified by the addition of about", 10

25% of phenol formaldehyde, a layer of vmethyl methacrylate resin bonded to said reinforcing layer on the exposed side of the denture, and a layer of mixed plastic bonded to said reinforcing layer on the tissue side of the denture, said mixed plastic comprising a mixture of methyl methacrylate and sufficient polystyrene to reduce the water absorption coecient.

5. The laminated denture of claim-4 wherein said mixed plastic is the product obtained by cur- 15 Number ing a mixture of about four parts of polymeric methyl methacrylate and about one part of a liquid containing about 80% of monomeric styrene and about 20% of monomeric methyl methacrylate.

LA MAR W. HARRIS. LLOYD W. COLTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 2,312,227 Yant Feb. 23. 1943 1,945,767 Bergerh'ausen et al. Feb. 6, 1934 2,013,295 Tidd Sept. 3, 1935 2,036,678 Blake Apr. 7, 1936 20 2,341,604 Dresch Feb. 15. 1944 

